Galvanic cells without transference

A nonzero OCV of a galvanic cell implies that the potential of one of the electrodes is more positive than that of the other (there is a positive and a negative electrode). For the galvanic cell without transference, the OCV can be written as... 

Electrochemical Cell Without Transference Assume that we want to determine the activities of HCl solutions of various concentrations. We assemble a galvanic cell with hydrogen and calomel electrode ... 

In the previous chapters the condition of electroneutrality was applied to all systems that contained charged species. In this chapter we study the results when this condition is relaxed. This leads to studies of electrochemical systems, especially those involving galvanic cells. Cells without transference are emphasized, although simple cells with transference are discussed. At the end of the chapter the conditions of equilibrium across membranes in electrochemical systems are outlined. 

In Chapter 10 standard potentials were obtained from measurements on galvanic cells involving only one electrolyte. These cells without transference thus do not involve surfaces between solutions of electrolytes, more commonly called liquid junctions. Although the measurements on cells without liquid junctions can be much more readily interpreted than the results from cells containing such boundaries most of the earlier work was carried out with the latter type of cell. Thus for instance instead of measuring the potential of the cell ... 

Concentration cells are a useful example demonstrating the difference between galvanic cells with and without transfer. These cells consist of chemically identical electrodes, each in a solution with a different activity of potential-determining ions, and are discussed on page 171. 

Semiconductor electrodes can be used in galvanic cells like metal electrodes and a controlled electrode potential can be applied by means of a potentiostat, if the electrode can be contacted with a suitable metal without formation of a barrier layer (ohmic contact). Suitable techniques for ohmic contacts have been worked out in connection with semiconductor electronics. Surface treatment is important for the properties of semiconductor electrodes in all kind of charge transfer processes and especially in the photoresponse. Mechanical polishing generates a great number of new electronic states underneath the surface 29> which can act as quenchers for excited molecules at the interface. Therefore, sufficient etching is imperative for studying photocurrents caused by excited dyes. 

Transference numbers will also be found useful in obtaining precise values of the activities of ion constituents. It was another of Arrhenius tacit assumptions that ion concentrations may be used without error in the law of mass action. To investigate the limits of validity of that assumption, and to lay a foundation for the modern interionic attraction theory of solutions, it is necessary to consider the thermodynamics of solutions, and of the galvanic cell, subjects which are discussed in Chapters 5 and 6. 

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